/*
 * Copyright (c) 1997, 2015, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 *
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 *
 *
 *
 */

package java.security;

import java.util.ArrayList;
import java.util.List;
import sun.security.util.Debug;
import sun.security.util.SecurityConstants;


/**
 * An AccessControlContext is used to make system resource access decisions
 * based on the context it encapsulates.
 *
 * <p>More specifically, it encapsulates a context and
 * has a single method, {@code checkPermission},
 * that is equivalent to the {@code checkPermission} method
 * in the AccessController class, with one difference: The AccessControlContext
 * {@code checkPermission} method makes access decisions based on the
 * context it encapsulates,
 * rather than that of the current execution thread.
 *
 * <p>Thus, the purpose of AccessControlContext is for those situations where
 * a security check that should be made within a given context
 * actually needs to be done from within a
 * <i>different</i> context (for example, from within a worker thread).
 *
 * <p> An AccessControlContext is created by calling the
 * {@code AccessController.getContext} method.
 * The {@code getContext} method takes a "snapshot"
 * of the current calling context, and places
 * it in an AccessControlContext object, which it returns. A sample call is
 * the following:
 *
 * <pre>
 *   AccessControlContext acc = AccessController.getContext()
 * </pre>
 *
 * <p>
 * Code within a different context can subsequently call the
 * {@code checkPermission} method on the
 * previously-saved AccessControlContext object. A sample call is the
 * following:
 *
 * <pre>
 *   acc.checkPermission(permission)
 * </pre>
 *
 * @author Roland Schemers
 * @see AccessController
 */

public final class AccessControlContext {

  private ProtectionDomain context[];
  // isPrivileged and isAuthorized are referenced by the VM - do not remove
  // or change their names
  private boolean isPrivileged;
  private boolean isAuthorized = false;

  // Note: This field is directly used by the virtual machine
  // native codes. Don't touch it.
  private AccessControlContext privilegedContext;

  private DomainCombiner combiner = null;

  // limited privilege scope
  private Permission permissions[];
  private AccessControlContext parent;
  private boolean isWrapped;

  // is constrained by limited privilege scope?
  private boolean isLimited;
  private ProtectionDomain limitedContext[];

  private static boolean debugInit = false;
  private static Debug debug = null;

  static Debug getDebug() {
    if (debugInit) {
      return debug;
    } else {
      if (Policy.isSet()) {
        debug = Debug.getInstance("access");
        debugInit = true;
      }
      return debug;
    }
  }

  /**
   * Create an AccessControlContext with the given array of ProtectionDomains.
   * Context must not be null. Duplicate domains will be removed from the
   * context.
   *
   * @param context the ProtectionDomains associated with this context. The non-duplicate domains
   * are copied from the array. Subsequent changes to the array will not affect this
   * AccessControlContext.
   * @throws NullPointerException if {@code context} is {@code null}
   */
  public AccessControlContext(ProtectionDomain context[]) {
    if (context.length == 0) {
      this.context = null;
    } else if (context.length == 1) {
      if (context[0] != null) {
        this.context = context.clone();
      } else {
        this.context = null;
      }
    } else {
      List<ProtectionDomain> v = new ArrayList<>(context.length);
      for (int i = 0; i < context.length; i++) {
        if ((context[i] != null) && (!v.contains(context[i]))) {
          v.add(context[i]);
        }
      }
      if (!v.isEmpty()) {
        this.context = new ProtectionDomain[v.size()];
        this.context = v.toArray(this.context);
      }
    }
  }

  /**
   * Create a new {@code AccessControlContext} with the given
   * {@code AccessControlContext} and {@code DomainCombiner}.
   * This constructor associates the provided
   * {@code DomainCombiner} with the provided
   * {@code AccessControlContext}.
   *
   * <p>
   *
   * @param acc the {@code AccessControlContext} associated with the provided {@code
   * DomainCombiner}.
   * @param combiner the {@code DomainCombiner} to be associated with the provided {@code
   * AccessControlContext}.
   * @throws NullPointerException if the provided {@code context} is {@code null}.
   * @throws SecurityException if a security manager is installed and the caller does not have the
   * "createAccessControlContext" {@link SecurityPermission}
   * @since 1.3
   */
  public AccessControlContext(AccessControlContext acc,
      DomainCombiner combiner) {

    this(acc, combiner, false);
  }

  /**
   * package private to allow calls from ProtectionDomain without performing
   * the security check for {@linkplain SecurityConstants.CREATE_ACC_PERMISSION}
   * permission
   */
  AccessControlContext(AccessControlContext acc,
      DomainCombiner combiner,
      boolean preauthorized) {
    if (!preauthorized) {
      SecurityManager sm = System.getSecurityManager();
      if (sm != null) {
        sm.checkPermission(SecurityConstants.CREATE_ACC_PERMISSION);
        this.isAuthorized = true;
      }
    } else {
      this.isAuthorized = true;
    }

    this.context = acc.context;

    // we do not need to run the combine method on the
    // provided ACC.  it was already "combined" when the
    // context was originally retrieved.
    //
    // at this point in time, we simply throw away the old
    // combiner and use the newly provided one.
    this.combiner = combiner;
  }

  /**
   * package private for AccessController
   *
   * This "argument wrapper" context will be passed as the actual context
   * parameter on an internal doPrivileged() call used in the implementation.
   */
  AccessControlContext(ProtectionDomain caller, DomainCombiner combiner,
      AccessControlContext parent, AccessControlContext context,
      Permission[] perms) {
        /*
         * Combine the domains from the doPrivileged() context into our
         * wrapper context, if necessary.
         */
    ProtectionDomain[] callerPDs = null;
    if (caller != null) {
      callerPDs = new ProtectionDomain[]{caller};
    }
    if (context != null) {
      if (combiner != null) {
        this.context = combiner.combine(callerPDs, context.context);
      } else {
        this.context = combine(callerPDs, context.context);
      }
    } else {
            /*
             * Call combiner even if there is seemingly nothing to combine.
             */
      if (combiner != null) {
        this.context = combiner.combine(callerPDs, null);
      } else {
        this.context = combine(callerPDs, null);
      }
    }
    this.combiner = combiner;

    Permission[] tmp = null;
    if (perms != null) {
      tmp = new Permission[perms.length];
      for (int i = 0; i < perms.length; i++) {
        if (perms[i] == null) {
          throw new NullPointerException("permission can't be null");
        }

                /*
                 * An AllPermission argument is equivalent to calling
                 * doPrivileged() without any limit permissions.
                 */
        if (perms[i].getClass() == AllPermission.class) {
          parent = null;
        }
        tmp[i] = perms[i];
      }
    }

        /*
         * For a doPrivileged() with limited privilege scope, initialize
         * the relevant fields.
         *
         * The limitedContext field contains the union of all domains which
         * are enclosed by this limited privilege scope. In other words,
         * it contains all of the domains which could potentially be checked
         * if none of the limiting permissions implied a requested permission.
         */
    if (parent != null) {
      this.limitedContext = combine(parent.context, parent.limitedContext);
      this.isLimited = true;
      this.isWrapped = true;
      this.permissions = tmp;
      this.parent = parent;
      this.privilegedContext = context; // used in checkPermission2()
    }
    this.isAuthorized = true;
  }


  /**
   * package private constructor for AccessController.getContext()
   */

  AccessControlContext(ProtectionDomain context[],
      boolean isPrivileged) {
    this.context = context;
    this.isPrivileged = isPrivileged;
    this.isAuthorized = true;
  }

  /**
   * Constructor for JavaSecurityAccess.doIntersectionPrivilege()
   */
  AccessControlContext(ProtectionDomain[] context,
      AccessControlContext privilegedContext) {
    this.context = context;
    this.privilegedContext = privilegedContext;
    this.isPrivileged = true;
  }

  /**
   * Returns this context's context.
   */
  ProtectionDomain[] getContext() {
    return context;
  }

  /**
   * Returns true if this context is privileged.
   */
  boolean isPrivileged() {
    return isPrivileged;
  }

  /**
   * get the assigned combiner from the privileged or inherited context
   */
  DomainCombiner getAssignedCombiner() {
    AccessControlContext acc;
    if (isPrivileged) {
      acc = privilegedContext;
    } else {
      acc = AccessController.getInheritedAccessControlContext();
    }
    if (acc != null) {
      return acc.combiner;
    }
    return null;
  }

  /**
   * Get the {@code DomainCombiner} associated with this
   * {@code AccessControlContext}.
   *
   * <p>
   *
   * @return the {@code DomainCombiner} associated with this {@code AccessControlContext}, or {@code
   * null} if there is none.
   * @throws SecurityException if a security manager is installed and the caller does not have the
   * "getDomainCombiner" {@link SecurityPermission}
   * @since 1.3
   */
  public DomainCombiner getDomainCombiner() {

    SecurityManager sm = System.getSecurityManager();
    if (sm != null) {
      sm.checkPermission(SecurityConstants.GET_COMBINER_PERMISSION);
    }
    return getCombiner();
  }

  /**
   * package private for AccessController
   */
  DomainCombiner getCombiner() {
    return combiner;
  }

  boolean isAuthorized() {
    return isAuthorized;
  }

  /**
   * Determines whether the access request indicated by the
   * specified permission should be allowed or denied, based on
   * the security policy currently in effect, and the context in
   * this object. The request is allowed only if every ProtectionDomain
   * in the context implies the permission. Otherwise the request is
   * denied.
   *
   * <p>
   * This method quietly returns if the access request
   * is permitted, or throws a suitable AccessControlException otherwise.
   *
   * @param perm the requested permission.
   * @throws AccessControlException if the specified permission is not permitted, based on the
   * current security policy and the context encapsulated by this object.
   * @throws NullPointerException if the permission to check for is null.
   */
  public void checkPermission(Permission perm)
      throws AccessControlException {
    boolean dumpDebug = false;

    if (perm == null) {
      throw new NullPointerException("permission can't be null");
    }
    if (getDebug() != null) {
      // If "codebase" is not specified, we dump the info by default.
      dumpDebug = !Debug.isOn("codebase=");
      if (!dumpDebug) {
        // If "codebase" is specified, only dump if the specified code
        // value is in the stack.
        for (int i = 0; context != null && i < context.length; i++) {
          if (context[i].getCodeSource() != null &&
              context[i].getCodeSource().getLocation() != null &&
              Debug.isOn("codebase=" + context[i].getCodeSource().getLocation().toString())) {
            dumpDebug = true;
            break;
          }
        }
      }

      dumpDebug &= !Debug.isOn("permission=") ||
          Debug.isOn("permission=" + perm.getClass().getCanonicalName());

      if (dumpDebug && Debug.isOn("stack")) {
        Thread.dumpStack();
      }

      if (dumpDebug && Debug.isOn("domain")) {
        if (context == null) {
          debug.println("domain (context is null)");
        } else {
          for (int i = 0; i < context.length; i++) {
            debug.println("domain " + i + " " + context[i]);
          }
        }
      }
    }

        /*
         * iterate through the ProtectionDomains in the context.
         * Stop at the first one that doesn't allow the
         * requested permission (throwing an exception).
         *
         */

        /* if ctxt is null, all we had on the stack were system domains,
           or the first domain was a Privileged system domain. This
           is to make the common case for system code very fast */

    if (context == null) {
      checkPermission2(perm);
      return;
    }

    for (int i = 0; i < context.length; i++) {
      if (context[i] != null && !context[i].implies(perm)) {
        if (dumpDebug) {
          debug.println("access denied " + perm);
        }

        if (Debug.isOn("failure") && debug != null) {
          // Want to make sure this is always displayed for failure,
          // but do not want to display again if already displayed
          // above.
          if (!dumpDebug) {
            debug.println("access denied " + perm);
          }
          Thread.dumpStack();
          final ProtectionDomain pd = context[i];
          final Debug db = debug;
          AccessController.doPrivileged(new PrivilegedAction<Void>() {
            public Void run() {
              db.println("domain that failed " + pd);
              return null;
            }
          });
        }
        throw new AccessControlException("access denied " + perm, perm);
      }
    }

    // allow if all of them allowed access
    if (dumpDebug) {
      debug.println("access allowed " + perm);
    }

    checkPermission2(perm);
  }

  /*
   * Check the domains associated with the limited privilege scope.
   */
  private void checkPermission2(Permission perm) {
    if (!isLimited) {
      return;
    }

        /*
         * Check the doPrivileged() context parameter, if present.
         */
    if (privilegedContext != null) {
      privilegedContext.checkPermission2(perm);
    }

        /*
         * Ignore the limited permissions and parent fields of a wrapper
         * context since they were already carried down into the unwrapped
         * context.
         */
    if (isWrapped) {
      return;
    }

        /*
         * Try to match any limited privilege scope.
         */
    if (permissions != null) {
      Class<?> permClass = perm.getClass();
      for (int i = 0; i < permissions.length; i++) {
        Permission limit = permissions[i];
        if (limit.getClass().equals(permClass) && limit.implies(perm)) {
          return;
        }
      }
    }

        /*
         * Check the limited privilege scope up the call stack or the inherited
         * parent thread call stack of this ACC.
         */
    if (parent != null) {
            /*
             * As an optimization, if the parent context is the inherited call
             * stack context from a parent thread then checking the protection
             * domains of the parent context is redundant since they have
             * already been merged into the child thread's context by
             * optimize(). When parent is set to an inherited context this
             * context was not directly created by a limited scope
             * doPrivileged() and it does not have its own limited permissions.
             */
      if (permissions == null) {
        parent.checkPermission2(perm);
      } else {
        parent.checkPermission(perm);
      }
    }
  }

  /**
   * Take the stack-based context (this) and combine it with the
   * privileged or inherited context, if need be. Any limited
   * privilege scope is flagged regardless of whether the assigned
   * context comes from an immediately enclosing limited doPrivileged().
   * The limited privilege scope can indirectly flow from the inherited
   * parent thread or an assigned context previously captured by getContext().
   */
  AccessControlContext optimize() {
    // the assigned (privileged or inherited) context
    AccessControlContext acc;
    DomainCombiner combiner = null;
    AccessControlContext parent = null;
    Permission[] permissions = null;

    if (isPrivileged) {
      acc = privilegedContext;
      if (acc != null) {
                /*
                 * If the context is from a limited scope doPrivileged() then
                 * copy the permissions and parent fields out of the wrapper
                 * context that was created to hold them.
                 */
        if (acc.isWrapped) {
          permissions = acc.permissions;
          parent = acc.parent;
        }
      }
    } else {
      acc = AccessController.getInheritedAccessControlContext();
      if (acc != null) {
                /*
                 * If the inherited context is constrained by a limited scope
                 * doPrivileged() then set it as our parent so we will process
                 * the non-domain-related state.
                 */
        if (acc.isLimited) {
          parent = acc;
        }
      }
    }

    // this.context could be null if only system code is on the stack;
    // in that case, ignore the stack context
    boolean skipStack = (context == null);

    // acc.context could be null if only system code was involved;
    // in that case, ignore the assigned context
    boolean skipAssigned = (acc == null || acc.context == null);
    ProtectionDomain[] assigned = (skipAssigned) ? null : acc.context;
    ProtectionDomain[] pd;

    // if there is no enclosing limited privilege scope on the stack or
    // inherited from a parent thread
    boolean skipLimited = ((acc == null || !acc.isWrapped) && parent == null);

    if (acc != null && acc.combiner != null) {
      // let the assigned acc's combiner do its thing
      if (getDebug() != null) {
        debug.println("AccessControlContext invoking the Combiner");
      }

      // No need to clone current and assigned.context
      // combine() will not update them
      combiner = acc.combiner;
      pd = combiner.combine(context, assigned);
    } else {
      if (skipStack) {
        if (skipAssigned) {
          calculateFields(acc, parent, permissions);
          return this;
        } else if (skipLimited) {
          return acc;
        }
      } else if (assigned != null) {
        if (skipLimited) {
          // optimization: if there is a single stack domain and
          // that domain is already in the assigned context; no
          // need to combine
          if (context.length == 1 && context[0] == assigned[0]) {
            return acc;
          }
        }
      }

      pd = combine(context, assigned);
      if (skipLimited && !skipAssigned && pd == assigned) {
        return acc;
      } else if (skipAssigned && pd == context) {
        calculateFields(acc, parent, permissions);
        return this;
      }
    }

    // Reuse existing ACC
    this.context = pd;
    this.combiner = combiner;
    this.isPrivileged = false;

    calculateFields(acc, parent, permissions);
    return this;
  }


  /*
   * Combine the current (stack) and assigned domains.
   */
  private static ProtectionDomain[] combine(ProtectionDomain[] current,
      ProtectionDomain[] assigned) {

    // current could be null if only system code is on the stack;
    // in that case, ignore the stack context
    boolean skipStack = (current == null);

    // assigned could be null if only system code was involved;
    // in that case, ignore the assigned context
    boolean skipAssigned = (assigned == null);

    int slen = (skipStack) ? 0 : current.length;

    // optimization: if there is no assigned context and the stack length
    // is less then or equal to two; there is no reason to compress the
    // stack context, it already is
    if (skipAssigned && slen <= 2) {
      return current;
    }

    int n = (skipAssigned) ? 0 : assigned.length;

    // now we combine both of them, and create a new context
    ProtectionDomain pd[] = new ProtectionDomain[slen + n];

    // first copy in the assigned context domains, no need to compress
    if (!skipAssigned) {
      System.arraycopy(assigned, 0, pd, 0, n);
    }

    // now add the stack context domains, discarding nulls and duplicates
    outer:
    for (int i = 0; i < slen; i++) {
      ProtectionDomain sd = current[i];
      if (sd != null) {
        for (int j = 0; j < n; j++) {
          if (sd == pd[j]) {
            continue outer;
          }
        }
        pd[n++] = sd;
      }
    }

    // if length isn't equal, we need to shorten the array
    if (n != pd.length) {
      // optimization: if we didn't really combine anything
      if (!skipAssigned && n == assigned.length) {
        return assigned;
      } else if (skipAssigned && n == slen) {
        return current;
      }
      ProtectionDomain tmp[] = new ProtectionDomain[n];
      System.arraycopy(pd, 0, tmp, 0, n);
      pd = tmp;
    }

    return pd;
  }


  /*
   * Calculate the additional domains that could potentially be reached via
   * limited privilege scope. Mark the context as being subject to limited
   * privilege scope unless the reachable domains (if any) are already
   * contained in this domain context (in which case any limited
   * privilege scope checking would be redundant).
   */
  private void calculateFields(AccessControlContext assigned,
      AccessControlContext parent, Permission[] permissions) {
    ProtectionDomain[] parentLimit = null;
    ProtectionDomain[] assignedLimit = null;
    ProtectionDomain[] newLimit;

    parentLimit = (parent != null) ? parent.limitedContext : null;
    assignedLimit = (assigned != null) ? assigned.limitedContext : null;
    newLimit = combine(parentLimit, assignedLimit);
    if (newLimit != null) {
      if (context == null || !containsAllPDs(newLimit, context)) {
        this.limitedContext = newLimit;
        this.permissions = permissions;
        this.parent = parent;
        this.isLimited = true;
      }
    }
  }


  /**
   * Checks two AccessControlContext objects for equality.
   * Checks that <i>obj</i> is
   * an AccessControlContext and has the same set of ProtectionDomains
   * as this context.
   * <P>
   *
   * @param obj the object we are testing for equality with this object.
   * @return true if <i>obj</i> is an AccessControlContext, and has the same set of
   * ProtectionDomains as this context, false otherwise.
   */
  public boolean equals(Object obj) {
    if (obj == this) {
      return true;
    }

    if (!(obj instanceof AccessControlContext)) {
      return false;
    }

    AccessControlContext that = (AccessControlContext) obj;

    if (!equalContext(that)) {
      return false;
    }

    if (!equalLimitedContext(that)) {
      return false;
    }

    return true;
  }

  /*
   * Compare for equality based on state that is free of limited
   * privilege complications.
   */
  private boolean equalContext(AccessControlContext that) {
    if (!equalPDs(this.context, that.context)) {
      return false;
    }

    if (this.combiner == null && that.combiner != null) {
      return false;
    }

    if (this.combiner != null && !this.combiner.equals(that.combiner)) {
      return false;
    }

    return true;
  }

  private boolean equalPDs(ProtectionDomain[] a, ProtectionDomain[] b) {
    if (a == null) {
      return (b == null);
    }

    if (b == null) {
      return false;
    }

    if (!(containsAllPDs(a, b) && containsAllPDs(b, a))) {
      return false;
    }

    return true;
  }

  /*
   * Compare for equality based on state that is captured during a
   * call to AccessController.getContext() when a limited privilege
   * scope is in effect.
   */
  private boolean equalLimitedContext(AccessControlContext that) {
    if (that == null) {
      return false;
    }

        /*
         * If neither instance has limited privilege scope then we're done.
         */
    if (!this.isLimited && !that.isLimited) {
      return true;
    }

        /*
         * If only one instance has limited privilege scope then we're done.
         */
    if (!(this.isLimited && that.isLimited)) {
      return false;
    }

        /*
         * Wrapped instances should never escape outside the implementation
         * this class and AccessController so this will probably never happen
         * but it only makes any sense to compare if they both have the same
         * isWrapped state.
         */
    if ((this.isWrapped && !that.isWrapped) ||
        (!this.isWrapped && that.isWrapped)) {
      return false;
    }

    if (this.permissions == null && that.permissions != null) {
      return false;
    }

    if (this.permissions != null && that.permissions == null) {
      return false;
    }

    if (!(this.containsAllLimits(that) && that.containsAllLimits(this))) {
      return false;
    }

        /*
         * Skip through any wrapped contexts.
         */
    AccessControlContext thisNextPC = getNextPC(this);
    AccessControlContext thatNextPC = getNextPC(that);

        /*
         * The protection domains and combiner of a privilegedContext are
         * not relevant because they have already been included in the context
         * of this instance by optimize() so we only care about any limited
         * privilege state they may have.
         */
    if (thisNextPC == null && thatNextPC != null && thatNextPC.isLimited) {
      return false;
    }

    if (thisNextPC != null && !thisNextPC.equalLimitedContext(thatNextPC)) {
      return false;
    }

    if (this.parent == null && that.parent != null) {
      return false;
    }

    if (this.parent != null && !this.parent.equals(that.parent)) {
      return false;
    }

    return true;
  }

  /*
   * Follow the privilegedContext link making our best effort to skip
   * through any wrapper contexts.
   */
  private static AccessControlContext getNextPC(AccessControlContext acc) {
    while (acc != null && acc.privilegedContext != null) {
      acc = acc.privilegedContext;
      if (!acc.isWrapped) {
        return acc;
      }
    }
    return null;
  }

  private static boolean containsAllPDs(ProtectionDomain[] thisContext,
      ProtectionDomain[] thatContext) {
    boolean match = false;

    //
    // ProtectionDomains within an ACC currently cannot be null
    // and this is enforced by the constructor and the various
    // optimize methods. However, historically this logic made attempts
    // to support the notion of a null PD and therefore this logic continues
    // to support that notion.
    ProtectionDomain thisPd;
    for (int i = 0; i < thisContext.length; i++) {
      match = false;
      if ((thisPd = thisContext[i]) == null) {
        for (int j = 0; (j < thatContext.length) && !match; j++) {
          match = (thatContext[j] == null);
        }
      } else {
        Class<?> thisPdClass = thisPd.getClass();
        ProtectionDomain thatPd;
        for (int j = 0; (j < thatContext.length) && !match; j++) {
          thatPd = thatContext[j];

          // Class check required to avoid PD exposure (4285406)
          match = (thatPd != null &&
              thisPdClass == thatPd.getClass() && thisPd.equals(thatPd));
        }
      }
      if (!match) {
        return false;
      }
    }
    return match;
  }

  private boolean containsAllLimits(AccessControlContext that) {
    boolean match = false;
    Permission thisPerm;

    if (this.permissions == null && that.permissions == null) {
      return true;
    }

    for (int i = 0; i < this.permissions.length; i++) {
      Permission limit = this.permissions[i];
      Class<?> limitClass = limit.getClass();
      match = false;
      for (int j = 0; (j < that.permissions.length) && !match; j++) {
        Permission perm = that.permissions[j];
        match = (limitClass.equals(perm.getClass()) &&
            limit.equals(perm));
      }
      if (!match) {
        return false;
      }
    }
    return match;
  }


  /**
   * Returns the hash code value for this context. The hash code
   * is computed by exclusive or-ing the hash code of all the protection
   * domains in the context together.
   *
   * @return a hash code value for this context.
   */

  public int hashCode() {
    int hashCode = 0;

    if (context == null) {
      return hashCode;
    }

    for (int i = 0; i < context.length; i++) {
      if (context[i] != null) {
        hashCode ^= context[i].hashCode();
      }
    }

    return hashCode;
  }
}
